A worm that hit Facebook last December has resurfaced, a security researcher said today, and is now hijacking user accounts -- not only for that social networking service, but also for MySpace, Friendster, LiveJournal and others.

The Koobface worm is again making the rounds on Facebook, said Jamz Yaneza, a research project manager with Trend Micro Inc. "But this is an improved version with some interesting functions," he said.

Like the variant that hit Facebook late last year , the newest Koobface tries to dupe users into clicking on a link that's included in a message from a friend. Clicking on the link displays a fake error message claiming that Adobe System Inc.'s Flash is out of date, and prompts the user to download an update.

The update is nothing of the sort, but is instead an executable file that installs the Koobface worm.

"Koobface.az," as Trend pegged the worm, rifles through a compromised PC, sniffs out browser cookies associated with 10 different social networking sites, uses the usernames and passwords within those cookies to log on to each service, searches for the infected user's friends, and then sends those people messages that include a link to the worm.

Much of the message processing takes place on a remote server, said Yaneza, which the hackers control. That server communicates with each infected PC, receiving data and sending instructions. "This is pretty serious stuff," Yaneza said.

Trend Micro has identified more than 300 Internet protocol (IP) addresses hosting the worm, and although some have been blocked, others are still online. Those addresses are located in Asia, Yaneza said.

"This is maybe only in its early stages," he added, referring to the small but growing number of infections. "I'd call it fairly active at the moment."

Koobface.az isn't the only piece of malware to have struck Facebook recently. Trend, as well as other security vendors, have noted a pair of scams in the past week that targeted users of the popular service. The most recent sent messages to users claiming that friends had turned them in for violating Facebook's terms of service; when people clicked on the included link, they downloaded an application that spammed all friends with a similar message and may have harvested information from each Facebook account as it did so.

"I don't think this is a coincidence," said Yaneza, speaking of Koobface coming hard on the heels of other attacks against Facebook users. "[Cyber criminals] are looking at how these services are being used, and more importantly, their sizes," he said.

"Users need to be very, very careful about what they install when they're on these [social networking] services," Yaneza advised. "And they should be careful about how they use social networks and what information they put on them. The criminals are gleaning all the information they can and using it against you."

This story, "Koobface worm to users: Be my Facebook friend" was originally published by
Computerworld.